%%
%% The LaTeX Companion, 3ed
%%
%% Example 3-6-19 on page I-251 in "vertbars --- Adding bars to paragraphs".
%%
%% Copyright (C) 2022 Frank Mittelbach
%%
%% It may be distributed and/or modified under the conditions
%% of the LaTeX Project Public License, either version 1.3c
%% of this license or (at your option) any later version.
%%
%% See https://www.latex-project.org/lppl.txt for details.
%%

\documentclass{tlc3exa}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{171.0pt}

  \addtolength\textwidth{-25pt}  % for the bars in the example

  \usepackage{microtype} % improve h&j in example

%StartShownPreambleCommands
\usepackage{vertbars} \setlength\barwidth{1pt}
%StopShownPreambleCommands

\begin{document}
This paragraph has no bar.
\begin{vertbar}
  The environment always starts a new paragraph
  and can only contain full paragraphs.
  \begin{vertbar}
    Nesting is possible as shown here but only
    on paragraph boundaries.
  \end{vertbar}
  Breaks across columns or pages are also
  possible and the bar continues.
\end{vertbar}   Another paragraph without a bar.
\end{document}
